1700-number-of-students-unable-to-eat-lunch.js

/**
 * 1700. Number of Students Unable to Eat Lunch
 * https://leetcode.com/problems/number-of-students-unable-to-eat-lunch/
 * Difficulty: Easy
 *
 * The school cafeteria offers circular and square sandwiches at lunch break, referred to by
 * numbers 0 and 1 respectively. All students stand in a queue. Each student either prefers
 * square or circular sandwiches.
 *
 * The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches
 * are placed in a stack. At each step:
 * - If the student at the front of the queue prefers the sandwich on the top of the stack, they
 *   will take it and leave the queue.
 * - Otherwise, they will leave it and go to the queue's end.
 *
 * This continues until none of the queue students want to take the top sandwich and are thus
 * unable to eat.
 *
 * You are given two integer arrays students and sandwiches where sandwiches[i] is the type of
 * the ith sandwich in the stack (i = 0 is the top of the stack) and students[j] is the
 * preference of the jth student in the initial queue (j = 0 is the front of the queue).
 * Return the number of students that are unable to eat.
 */

/**
 * @param {number[]} students
 * @param {number[]} sandwiches
 * @return {number}
 */
var countStudents = function(students, sandwiches) {
  const preferenceCount = [0, 0];
  for (const pref of students) {
    preferenceCount[pref]++;
  }

  for (const sandwich of sandwiches) {
    if (preferenceCount[sandwich] === 0) {
      return preferenceCount[0] + preferenceCount[1];
    }
    preferenceCount[sandwich]--;
  }

  return 0;
};